This invention relates to strap retracting apparatus and more particularly to improvements in strap retracting apparatus of the type in which the belt strap is locked against any further protracting movement after it engages the body of a passenger.
A safely seat belt is provided for a seat in a vehicle such as an automobile or airplane, and this seat belt acts to securely hold the body of a passenger to the seat for ensuring his safety when an abrupt shock is imparted to the vehicle. The belt strap for engagement with the body of the passenger is housed within a cover case firmly fixed to a supporting member mounted to the floor of the vehicle or the like and the passenger can wear any desired length of the belt strap on his body by gripping the exposed end of the belt strap and pulling the belt strap out of the cover case.
As an example of prior art seat belt retractors, an automatic locking apparatus is known in which a locking mechanism is actuated as soon as a passenger wears the belt strap on his body so that it acts to prevent any further protraction of the belt strap. In this automatic locking apparatus, the outer diameter of the belt strap turns wound around the spool, slight retraction of the belt strap during manipulation for complete engagement of the belt strap on the wearer's body, or the like are utilized to actuate the locking mechanism, and various kinds of such locking mechanism are already known in the art. This automatic locking apparatus is very satisfactory in ensuring the safety of the passenger due to the fact that it locks completely the belt strap against any further protraction, but it has a defect as described below. Generally, a force for normally urging the belt strap in the retracting direction is imparted to the spool so as to cause automatic retraction of the belt strap into the cover case. This force acts to fasten the body of the passenger to the seat, but it is naturally not so large as to give an uncomfortable sense to the passenger. However, it is generally known that the passenger makes relatively large movement of his body after wearing the seat belt on his body, and following this movement of the passenger's body, the belt strap can only move in the retracting direction by being urged by the retracting force. As a result, the belt strap is locked again in the retracted position when the movement of the passenger's body exceeds a certain amount. Since the belt strap cannot be protracted any further even in this newly established re-locked state, the body of the passenger is tightly fastened in a state which differs from the initially established optimum state.
The belt strap moves a predetermined amount peculiar to the apparatus until it is fixed in the re-locked position, and this predetermined amount corresponds to one step of the locking mechanism which determines the belt length when the belt strap is worn on the body of the passenger. This one step is selected to be less than 25 mm in belt length in view of the demand that the belt length be finely adjusted as much as possible, and it is commonly selected to lie within the range of about 10 to 13 mm. As experience teaches, the movement of the passenger's body exceeds frequently the above-described limit of one step in terms of the belt length. Thus, the belt strap has been re-locked in the one-step retracted position each time the passenger moves his body and the passenger's body has been excessively fastened to such an extent that he feels uncomfortable. In order to alleviate this excessive state of fastening, the entire belt strap had to be released once to be retracted into the cover case and the belt wearing manipulation had to be carried out again. This defect has been an important reason which obstructs wide use of the safety seat belt of the automatic locking type.